1. Field of the Invention
This invention pertains to a fuel-flow alarm adapted to provide a warning signal when a fuel flow rate through a conduit is outside a predetermined permissible range, such as when the conduit is obstructed.
2. Discussion of the Prior Art
It is known in the art to equip marine and other engines with fuel-flow alarms. These alarms provide an indication of abnormalities in the free-flow of fuel through a conduit such as when foreign matter in the fuel clogs the fuel line or a fuel filter, or when the fuel line becomes kinked or obstructed. Such known alarms function by detecting the reduced pressure inside the fuel line downstream of the fuel filter. When a reduced pressure exceeding a certain level is detected, an audible buzzer or a visual lamp provides a warning signal to an operator. Such prior art alarm arrangements are represented by U.S. Pat. No. 4,870,392.
In these known fuel-flow alarms, the fuel line reduced pressure warning is based on high-load engine operating conditions. The reason for this is that if the fuel line reduced pressure warning were based on low load or low RPM operating conditions, the reduced pressure setting would have to be a low one, and if that setting were used, high load or high RPM operations would exceed these normal limits and the alarm would sound when the fuel line was not actually obstructed. The high load operating premise was used, therefore, to avoid this contingency.
Because of the warning pressure setting problem noted above, the fuel-flow alarms of the prior art simply do not operate during low load or low RPM engine operating conditions. Instead, these fuel-flow alarms function only when the engine is operating under high load or high RPM conditions, and do not function at all under low load or low RPM operating conditions.
When used in small marine engines, for example, after trolling for a long period of time and subsequently operating the engine at full speed to return to harbor, such known alarms would not sound even if the fuel line was obstructed during the trolling operation. It would only sound during full speed engine operating conditions. If the alarm is activated and the operator was to ignore the warning and return to harbor at full speed, the engine could be damaged due to, for example, an excessively lean fuel charge caused by partial fuel shortage. Accordingly, the only alternative would be to return to harbor at a low speed.